1. Field of Invention
The present invention relates to a method of fabricating an integrated circuit. More particularly, the present invention relates to a fabricating method for forming a glue layer and a barrier layer.
2. Description of Related Art
Among all metal materials, tungsten has an advantageous high melting point, heat expansion ratio, and correspondence to silicon. In addition, tungsten deposited by chemical vapor deposition (CVD) does not have a high internal stress, and has a better step coverage. Thus, the manufacture of a metal plug with tungsten deposited by CVD has been widely used in the secondary micrometer process.
It is well known that a glue layer, also known as a barrier layer is formed between the surface of a contact opening or via opening and the metal plug to improve the adhesion between the tungsten plug and other materials. For example, TiN.sub.x is most often used as the material for glue layer in the present process. However, a metal nitride layer is usually added below the TiN.sub.x so that the contact resistance between the TiN.sub.x and bottom material of the contact opening or via opening is reduced.
The Ti layer and the TiN.sub.x layer are usually deposited by sputtering in the process of the integrated circuits. However, the TiN.sub.x layer formed by sputtering has poor step coverage and poor filling. To improve the step coverage and the filling of the TiN.sub.x layer, the TiN.sub.x layer is deposited by a collimator sputtering. Thus, this improves the deposition by sputtering at the bottom of the contact opening or via opening.
However, there is limited step coverage to the bottom corner of the contact opening and via opening with the above method. The TiN.sub.x layer is unable to completely cover the Ti layer below while part of the Ti layer is exposed.
Since WF.sub.6 serves as the gas source for CVD in the subsequent tungsten deposition. When the lower Ti layer is exposed due to the poor step coverage of the TiN.sub.x layer or any defect in the TiN.sub.x layer, F atoms released by WF.sub.6 can then pass through the TiN.sub.x layer and react with Ti located below to form TiF.sub.4. As TiF.sub.4 is a volatile gas, a phenomenon similar to an explosion will occur when tungsten is deposited on the contact window or via opening. This is known as a volcano effect. The occurrence of such effect results in removal or bending of the TiN.sub.x layer, allowing tungsten to be deposited on both sides of the TiN.sub.x layer that are removed. If this occurs on the top end corner of the contact opening or via opening, there will be a projection of the surface of the tungsten layer. When the projection is too severe, it is not easily removed by usual reactive etching process. As a result, this leads to the problems of blind window, short circuit, wafer pollution, and low yield.
Conventionally, the rapid thermal process (RTP) is usually performed in the N.sub.2 or NH.sub.3 based surroundings to prevent the above from occurring during the manufacture of the contact opening. This performs a nitridation reaction to the exposed Ti layer. However, in view of the thermal budget of the lower metal layer, it is not appropriate to perform a nitridation reaction to the Ti layer with the above RTP.